Direct material deposition processes allow complex components to be efficiently fabricated in small lot sizes to meet the stringent requirements of the rapidly changing manufacturing environment. This process produces three-dimensional parts directly from a computer aided design (CAD) solid model. U.S. Pat. No. 4,323,756 teaches that complex, net-shaped objects can be built by sequential layer deposition of feedstock material in powder or wire form, whereby the material is directed into a focused laser beam, melted, and deposited onto a deposition substrate to generate solid objects of varying three-dimensional complexity in a layer-wise manner. Other prior art using this method includes xe2x80x9cUsing the Laser Engineered Net Shaping (LENS(trademark)) Process to Produce Complex Components from a CAD Solid Modelxe2x80x9d by D. M. Keicher et al. in SPIE Conference, San Jose, Calif., January 1997. This method of direct material fabrication uses a single nozzle or powder delivery system that introduces a converging stream of powdered material into the laser beam at or near the beam""s minimum diameter (i.e. focus or focal plane). The stream is at an angle off-normal to a deposition surface whereby uniform geometries of three-dimensional objects can be produced by providing computer controlled motion of the deposition surface relative to the laser beam. The prior art for this technology in general has focused on methods and approaches to enable the deposition process; however, there is little data available on how best to control these processes to achieve the desired outcome in the solid structure.
U.S. Pat. No. 5,043,548 discloses a laser plasma spraying nozzle and method that permits high deposition rates and efficiencies of finely divided particles of a wide range of feed materials. This system uses powdered materials that are carried to the interaction regions via a carrier gas and lasers to melt these particles. However, this system relies solely on the use of a plasma to melt the particles before they are ever introduced to the deposition region. In fact, the carrier gas is often a mixture which promotes ionization, and, as such, the formation of a plasma. The plasma serves to melt the powder particles before they ever come into contact with the deposition substrate. In addition, the beam is diverging such that when it does impact the deposition substrate, the beam irradiance is sufficiently low so that no melting of the deposition substrate occurs. A great distance between the focal point of the laser and the central portion of the plasma is maintained to prevent the substrate from melting. This distance, ranging from 1-6 inches, is a characteristic of this apparatus. The materials are deposited in either a liquid or gaseous state. This design provides a unique method for coating parts; however, it has never been intended for fabrication of multi-layered parts. Due to the diverging nature of the powder material, this plasma technique fails to provide the feature definition necessary for fabricating complex, net-shaped objects. In this patent, the inventors describe several process conditions used to successfully deposit materials in thin layers, yet there is no correlation drawn between the materials"" properties and the processing conditions. Another nozzle design is shown in U.S. Pat. No. 4,724,299. This nozzle design requires the powder to be delivered from an annular source that is coaxial with a single laser beam. This design provides a uniform feed of powder to the cladding region, a laser used as an energy source to melt the powder that is to be deposited, and a powder distribution system. However, this system requires that the powder distribution system be contained within the nozzle assembly.
This nozzle design is very specific to the laser cladding application. The term laser cladding is used specifically to imply surface modification and not the direct fabrication method. More importantly, the design relies on having an annular powder distribution channel to deliver the powder to the deposition region. The annular powder distribution region provides powder to the focused laser beam from all directions and does not concentrate the powder for a tightly focused powder stream. For a single laser beam that is coaxial to the powder flow, this nozzle should work well to provide a uniform layer and in fact may very likely be applied to directly fabricate metallic components from a CAD solid model. Again, however, there is no mention on how the process conditions will affect material properties.
U.S. Pat. No. 4,323,756 also covers the direct metal deposition (DMD) process. This technique uses both wires and powders as filler material. It also uses a single laser beam to deposit the various materials. This patent teaches that the volume of the feedstock material must be less than that of the melted substrate material. However, this reduces the rate of deposition and increases the time to produce parts. The requirement to limit the volume of the feedstock material to be less than that of the melted substrate material was driven by the desire to remove impurities and obtain epitaxial growth. Instead of removing impurities by continuously remelting the previously deposited materials, impurities can be efficiently eliminated by performing the deposition in a controlled atmosphere environment, such as a glove box. Furthermore, expitaxial growth is not desired in most three-dimensional parts, since it may result in anisotropic material characteristics. For most general applications, uniform material properties are desired that do not limit the feedstock volume to be less than that of the deposition substrate melted region. In fact, our data suggests that there may be advantages to minimizing heat input to the deposited substrate to enhance material properties.
U.S. Pat. No. 5,578,227 contains similarities to these other inventions, such as the use of a positioning system to direct the location of deposition, and the use of a laser to deposit the feedstock material. This patent uses a single laser beam for the deposition process and wire as the feedstock material. A critical claim of this patent that differentiates it from these others requires that the laser cause the feedstock material to bond to the previously deposited layer without substantially altering the cross-section of the newly deposited material. Such a continuous form of material would appear to be prone to substantial problems of warpage and distortion of the deposited layers due to an incomplete melting of the feedstock material. For the powder deposition processes, the feedstock material is completely consumed within the 3-D net shape, with the powder""s cross-section being substantially altered. Since only interfacial bonding of the feedstock material occurs, the material properties of the deposited material are not likely to be significantly altered. In addition, there is no discussion on how to control the properties of the material deposited using this technique.
Although casting processes could be used to produce embedded structures within a solid component, these processes would require that the material used to create the embedded structure be removed by some method after the component has been made.
A need exists to understanding these potentially useful processes and, in doing so, to develop a methodology to alter and control material properties during processing.
Accordingly, several objects and advantages of the present invention are:
(a) to provide a method to control the thermal properties of a solid structure;
(b) to provide a means to embed hollow and/or multi material structures within a normally solid component;
(c) to provide a means to locally control the thermal history of a structure;
(d) to provide high efficient heat transfer within structures;
(e) to provide a methodology to create components that allow the thermal characteristics of a structure to be engineered into a component by including embedded structures and/or varying materials within that structure; and
(f) to provide a means to control pressure drop across embedded structures.
These and other objects and advantages of the invention will become apparent upon review of the specification and appended claims.
The present invention provides internal features that can now easily be fabricated in components using direct material deposition techniques coupled with a layer wise manufacturing approach. These features provide thermal control of complex shapes, in ways not previously available. One particular area of impact for this invention is in providing high efficiency cooling for injection mold tooling. This technology provides the ability to create an isothermal surface as well as to provide thermal gradients for controlled thermal processes. The invention describes features and methods that are obtainable by using material deposition manufacturing techniques as well as material sintering techniques. The recent development of precise material deposition processes provides the ability to create structures and material combinations that were previously not viable for manufacture. Traditional methods can not be used for manufacturing of these internal geomtries and multiple material structures such that they are completely enclosed in a solid body.
The use of embedded structures for conformal cooling channels is absolutely beneficial to rapidly and uniformly cooling many complex shapes, both external and internal. These geometries will be limited to certain manufacturing technologies, but will have a wide variety of applications.